Efficient am rlc re-establishment mechanism

ABSTRACT

A re-establishment method for an Acknowledged Mode Radio Link Control entity, the method comprising: receiving, from an upper entity, a command to perform Acknowledged Mode Radio Link Control re-establishment; and managing control protocol data units by considering the direction of the Acknowledged Mode Radio Link Control re-establishment, wherein control protocol data units related to the direction are deleted and control protocol data units not related to the direction are not deleted.

TECHNICAL FIELD

The present invention relates to an operation method of an AM RLC in aUMTS (Universal Mobile Telecommunications System), which is a Europeantype IMT-2000 system. In particular, the present invention relates to animproved AM RLC re-establishment method, whereby when the RLC entity isre-established, the AM RLC reduces the (number of amount of) data orcontrol messages to be deleted, to thus minimize discontinuouscommunications and can increase data transmission and reception rates.

BACKGROUND ART

FIG. 1 shows an exemplary network architecture for UMTS (UniversalMobile Telecommunications System). The UMTS system is generallycomprised of mobile terminals (user equipment: UE), a UTRAN (UMTSTerrestrial Radio Access Network), and a core network (CN). The UTRANhas one or more radio network sub-systems (RNS), with each RNS having aradio network controller (RNC) and one or more base stations (Node Bs).For each Node B, one or more cells exist.

FIG. 2 shows an exemplary radio protocol architecture used in UMTS.These radio protocol layers exist in the UE and UTRAN in pairs, andhandles data transmissions over the radio interface. With respect toeach radio protocol layer, the PHY layer (Layer 1) serves the purpose oftransmitting data over the radio interface by using various radiotransmission techniques. The PHY layer is connected with a MAC layer (ahigher level layer) via transport channels in order to support reliabledata transmissions, and the transport channel can be divided intodedicated transport channels and common transport channels according towhether or not the channels are shared.

In Layer 2, the MAC, RLC, PDCP and BMC layers exist. The MAC layerperforms mapping of various logical channels to various transportchannels, and also performs logical channel multiplexing for mappingmultiple logical channels to a single transport channel. The MAC layeris connected with the RLC layer (a higher level layer) via logicalchannels, and the logical channels are divided into control channels fortransmitting control plane information and traffic channels fortransmitting user plane information, according to the type of data beingtransmitted. The MAC layer can be further divided into a MAC-bsub-layer, a MAC-d sub-layer, a MACc/sh sub-layer, a MAC-hs sub-layer,and a MAC-e sub-layer according to the types of transport channels beingmanaged. The MAC-b sub-layer handles the management of a BCH (BroadcastChannel), which is a transport channel for handling the broadcast ofsystem information. The MAC-c/sh sub-layer manages common transportchannels such as a FACH (Forward Access Channel), a DSCH (DownlinkShared Channel), and the like that are shared by various mobileterminals. The MAC-d sub-layer handles the management of a DCH(Dedicated Channel) that is a dedicated transport channel for aparticular mobile terminal. The MAC-hs sub-layer manages a HS-DSCH (HighSpeed Downlink Shared Channel), which is a transport channel for highspeed downlink data transmission. The MAC-e sub-layer manages a E-DCH(Enhanced Dedicated Channel), which is a transport channel for highspeed uplink data transmission.

The RLC layer guarantees the quality of service (QoS) of each radiobearer (RB) and handles the transmission of data thereof. To guaranteethe QoS that is unique to an RB, the RLC layer has one or twoindependent RLC entities for each RB, and provides three types of RLCmodes, namely, TM (Transparent Mode), UM (Unacknowledged Mode), and AM(Acknowledged Mode) in order to support various QoS. Also, the RLC layerperforms the function of adjusting the size of data to be appropriatefor a lower level layer to transmit data over the radio interface. To doso, a function of segmentation and concatenation of data received from ahigher level layer is performed.

The PDCP layer is located at a higher level from the RLC layer, andemploys IP (Internet Protocol) packet formats (such as IPv4 or IPv6) toallow efficient data transmission over the radio interface having arelatively small bandwidth. To do so, the PDCP layer performs thefunction of header compression, which allows transmission of onlynecessary information in the header portion of the data, to thusincrease the transmission efficiency of the radio interface. As headercompression is the basic function, the PDCP layer only exists in the PSdomain, and in order to provide effective header compression withrespect to each PS service, one PDCP entity exists for each RB.

Additionally, in Layer 2, a BMC (Broadcast/Multicast Control) layerexists at a higher level from the RLC layer, and performs scheduling ofcell broadcast messages and performs the function of broadcasting tomobile terminals located in a particular cell. The RRC (Radio ResourceControl) layer located at the lowermost portion of Layer 3, is onlydefined in the control plane, controls the parameters of Layer 1 andLayer 2 that are related to the setup, reconfiguration, and release ofRBs, and also handles the control of logical channels, transportchannels, and physical channels. Here, the RB refers to a logical paththat is provided by Layer 1 and Layer 2 of the radio protocol for datatransfer between the mobile terminal and the UTRAN. In general, thesetup of an RB refers to the process of stipulating the characteristicsof a protocol layer and a channel required for providing a specificservice, and setting the respective detailed parameters and operationmethods.

The RLC layer that is related to the present invention will beconsidered in more detail.

A basic function of the RLC layer is to guarantee the QoS of each RB andto transmit data thereof. As the RB service is a service that the Layer2 of the radio protocol provides to a higher level, the entire Layer 2effects the QoS, and in particular, the effect of the RLC layer issignificant. To guarantee the QoS that is unique to the RB, the RLClayer has independent RLC entities for each RB, and provides three typesof RLC modes (TM, UM, AM) for supporting various QoS. These three modesof the RLC layer have differences in their operation methods because theQoS that they respectively support are different, and their detailedfunctions also have differences. As such, the RLC layer should beconsidered in more detail with respect to their operation modes.

The TM RLC is a mode in which no overhead is attached to the RLC SDUreceived from a higher level when forming (constituting) a RLC PDU.Namely, the name TM RLC refers to the fact that the RLC passes the SDUsin a transparent manner, and the following functions are performed inthe user plane and the control plane. In the user plane, because thedata processing time is short, transmission of real-time circuit data,such as voice or streaming of the circuit service (CS) domain, arehandled. In the control plane, because there is no overhead within theRLC, in case of the uplink, transmission of RRC messages fromunspecified mobile terminals are handled, while for the downlink,transmission of RRC messages that are broadcast to all mobile terminalswithin a cell are handled.

Unlike the transparent mode (TM), the mode in which overhead is added bythe RLC is called a non-transparent mode, which comprises two types ofmodes; unacknowledged mode (UM) that provides no response thatacknowledges receipt of transmitted data (UM), and acknowledged mode(AM) that provides a response. The UM RLC transmits each PDU upon addingthereto a PDU header that includes a sequence number (SN), to thus allowthe receiving side to know which PDUs were lost (or missing) duringtransmission. Due to such function, the UM RLC handles the transmissionof broadcast/multicast data in the user plane or the transmission ofreal-time packet data, such as voice (e.g., VoIP) or streaming of thepacket service (PS) domain, and in the control plane, the transmissionof RRC messages that do not need a reception acknowledgement responseamong the RRC messages transmitted to a particular terminal orparticular terminal group.

As a type of non-transparent mode, the AM RLC forms a PDU by adding aPDU header that includes a SN (as done in the UM RLC), but unlike the UMRLC and the significant difference therefrom is that the receiving sideprovides an acknowledgement for a PDU transmitted from the transmittingside. In AM RLC, the reason why the receiving side providesacknowledgement is to request the transmitting side to re-transmit thosePDUs that could not be received. Such re-transmission function is one ofthe most significant characteristics of the AM RLC. As a result, thepurpose of the AM RLC is to guarantee error-free data transmissionsthrough the re-transmitting function. Due to this purpose, the AM RLC,in the user plane, usually handles non-real-time packet datatransmissions (such as TCP/IP of the PS domain), and in the controlplane, handles the transmission of RRC messages that always requiresreception acknowledgement response among the RRC messages transmitted toa particular terminal within a cell.

With respect to directions, the TM RLC and UM RLC are used inuni-directional communications, while AM RLC is used in bi-directionalcommunications because there is feedback from the receiving side. Asbi-directional communications are generally used for point-to-pointcommunications, the AM RLC uses only a dedicated logical channel. Thereare also differences in structure, whereby for TM RLC and UM RLC, asingle RLC entity has one type of structure for either a transmitter orreceiver, but for AM RLC, a single RLC entity has both a transmitter anda receiver.

The AM RLC is complicated because of its re-transmission function. Formanaging re-transmission functions, the AM RLC has a re-transmissionbuffer in addition to a transmission/reception buffer, employs atransmission/reception window for flow control, performs a pollingfunction whereby the transmitter requests status information from thepeer RLC of the receiver, employs a status report sent by a receiver toreport its buffer state to a peer RLC of the transmitter, employs astatus PDU to carry the status information, performs a piggybackfunction that inserts a status PDU into a data PDU in order to increasedata transmission efficiency, and also performs many other functions. Inaddition, if the AM RLC entity discovers a significant error during itsoperation process, a Reset PDU is employed to request the peer AM RLCentity to re-set all operations and parameters, and a Reset Ack PDU isused for responding to such Reset PDU. Also, to support such functions,the AM RLC requires various protocol parameters, state variables, timer,and the like. The PDUs used for data transmission control in the AM RLC,such as a status report or status PDU, Reset PDU, etc. are calledControl PDUs, while the PDUs used for transferring user data are calledData PDUs.

To summarize, the PDUs used in AM RLC are divided into two types; DataPDUs and Control PDUs. There are four types of Control PDUs, namely, aStatus PDU, a Piggybacked Status PDU, a Reset PDU, and a Reset Ack PDU.

A Reset Procedure is one situation where a Control PDU is employed. TheReset Procedure is used to solve problems when there is an erroneoussituation in the operation of the AM RLC, such as when the sequencenumbers being respectively used are different, when a certain number oftransmission failures for a PDU or SDU occur, and the like. Upon usingthe Reset Procedure, the AM RLC of the receiver and of the transmitterinitialize the state variables such that a state where communication canbe performed again is achieved. The Reset Procedure is as follows.First, the side that determined to start the Reset Procedure, namely theAM RLC of the transmitter includes the transmission direction HFN (HyperFrame Number) that it currently uses into the Reset PDU and transmitssuch to the receiver. Then, upon receiving such Reset PDU, the AM RLC ofthe receiver resets its reception direction HFN value and alsoinitializes the sequence numbers and other various state variables.Also, the receiver AM RLC transmits a Reset Ack PDU that includes itstransmission direction HFN value to the transmitter AM RLC, and uponreceiving this Reset Ack PDU, the transmitter AM RLC initializes variousstate variables after resetting its reception direction HFN value.

FIG. 3 shows an exemplary structure of an RLC PDU used in an AM RLCentity. Here, the structure of an AMD PDU, which is a Data PDU used whentransmitting data.

The AMD PDU is used when the AM RLC entity is to transmit user data orto transmit piggybacked status information and a polling bit. The userdata portion comprises 8 bit integer multiples, and the AMD PDU headercomprises a sequence number having a size of 2 octets. Also, the headerportion of the AMD PDU includes a length indicator.

FIG. 4 shows an exemplary structure of a Status PDU. The Status PDU iscomprised of different types of super fields (SUFI). The Status PDU mayhave a variable size, but is limited to the size of the largest RLC PDUof the logical channel on which the Status PDU is transmitted. Here, theSUFI serves the purpose of providing certain information, such asindicating which AMD PDUs arrived at the receiver or which AMD PDUs havenot arrived. The SUFI may be comprised of three parts; type, length andvalue.

FIG. 5 shows an exemplary structure of a Piggybacked Status PDU. Thestructure of the Piggybacked Status PDU is similar to that of the AMDPDU, but the D/C field of the AMD PDU is replaced with a reserved bit(R2). The Piggybacked Status PDU is inserted if there is sufficientspace remaining in the AMD PDU. The PDU type value is always fixed to be000. Ultimately, a Control PDU includes both a Status PDU and aPiggybacked Status PDU.

FIG. 6 shows an exemplary structure of a Reset/Reset Ack PDU. The ResetPDU includes a 1 bit sequence number called an RSN. The Reset Ack PDU istransmitted in response to the received Reset PDU, and the RSN of thereceived Reset PDU is included when transmitting.

The following parameters are used in the Reset/Reset Ack PDU format.

(1) D/C field: indicates whether the PDU is a Control PDU or Data PDU

(2) PDU Type: indicates the type of Control PDU, namely, whether the PDUis a Reset PDU, Status PDU, etc.

(3) Sequence Number: refers to sequence number information of the AMDPDU.

(4) Polling Bit: set when requesting a Status Report from the receiver.

(5) Extension bit (E): indicates whether or not the next octet is alength indicator.

(6) Reserved bit (R1): if used in a Reset PDU or a Reset Ack PDU, codedas 000.

(7) Header extension (HE): indicates whether the next octet is a lengthindicator or data.

(8) Length indicator: indicates the location of a boundary, if suchboundary exists between respectively different SDUs within the dataportion of a PDU.

(9) PAD: indicates a padding region, but not used in the AMD PDU.

The Reset procedure for the AM RLC entity will be explained below.

First, when a situation where a Reset procedure needs to be performedoccurs, the receiver must send a Reset PDU to the transmitter. The Resetprocedures is performed if a Status PDU containing an erroneous sequencenumber is received or if a particular PDU transmission has failed acertain number of times. When a Reset PDU is transmitted, thetransmitter performs the following operations.

1. Transmission of the AMD PDU and Status PDU is stopped.

2. The received AMD RLC PDU, the Status PDU, and the Piggybacked StatusPDU are ignored.

3. The VR(RST) is incremented by 1.

4. If VR(RST) is greater than MaxRST, this is informed to the RRC, ifVR(RST) is less than MaxRST, the Reset PDU is transmitted to thereceiver.

Here, the VR(RST) is initialized by using internal parameters of thereceiver each time the reset procedure is performed. This value is themaximum value of transmitting the Reset PDU for each reset procedure.Namely, if the Reset PDU transmission exceeds the MaxRST value, thereset procedure is immediately terminated and the higher level isinformed that an unsolvable error has occurred.

When the transmitter transmits the Reset PDU, a HFNI value and a RSNvalue are included in the transmission. Here, the transmitter sets theHFNI as the maximum HFN value that it uses. The HFN is a values used inencoding (encryption) and the transmitter uses the HFN value to encodethe portions of the AMD PDU excluding the SN value of thereof. Thereceiver uses the same HFN value to decode the received AMD PDU. If thereceiver and the transmitter do not have the same HFN value,communication therebetween cannot be maintained. Accordingly, in thereset procedure, the transmitter and receiver exchange their HFN valuessuch that both the transmitter and receiver are set to have the same HFNvalue. Thus, the transmitter and the receiver include their HFN value inthe Reset PDU or the Reset Ack PDU when transmitting.

The RSN value is used for matching each of the Reset PDUs and the ResetAck PDUs. Namely, if the transmitter sent a Reset PDU with the RSN valueset to 1, the receiver recognizes only the Reset Ack PDU having the RSNset to 1 as its desired Reset Ack PDU. If a Reset Ack PDU with a RSNvalue set to a value other than 1 is received, such Reset Ack PDU isdeems as erroneous and is thus discarded. Also, for each reset procedurethat begins, the RSN value is increased by one.

When the Reset Ack PDU is transmitted in response to the Reset PDU, thereceiver sends the largest value HFN that is used in its transmissiondirection by filling it into the HFNI, and also, the same RSN value asthat included in the corresponding Reset PDU is included in the ResetAck PDU and transmitted.

Upon receiving the Reset PDU, the receiver performs the followingoperations.

1. The transmitter compares whether the RSN value used in the resetprocedure that was last performed with the RSN value included in thecurrently received Reset PDU are the same or not. Then, step 2 isperformed.

2. If the RSN values are the same in step 1, the receiver againtransmits a Reset Ack PDU using the same value as that for previouslytransmitting the Reset Ack PDU. Then, step 3 is performed.

3. If the currently received Reset PDU is the first Reset PDU receivedafter the RLC entity was established or re-established, or if the RSNvalues is different than that of the most recently received Reset PDU,then the following steps are sequentially performed; otherwise theprocess is terminated.

4. A Reset Ack PDU is newly formed and transmitted.

5. The state variables are initialized and the currently operating Timeris stopped.

6. The received RLC PDUs are discarded.

7. The RLC PDUs transmitted before the Reset are discarded.

8. The HFN of the receiver direction is set according to that in thereceived Reset PDU.

9. The HFN of the transmitter direction and of the receiver directionare increased by 1.

After the transmitter transmits the Reset PDU, a Reset Ack PDU is waitedto be received, and when the Reset Ack PDU is received, the followingoperations are performed by the transmitter.

1. If the RSN value included in the Reset Ack PDU is the same as the RSNvalue included in the Reset PDU that it transmitted, the following stepsare performed; otherwise, the Reset Ack PDU is discarded.

2. The HFN of the receiver direction is reset by using the HFNI valueincluded in the received Reset Ack PDU.

3. The state variables are initialized and the currently operating Timeris stopped.

4. The received RLC PDUs are discarded.

5. The RLC PDUs transmitted before the Reset are discarded.

6. The HFN of the transmitter direction and of the receiver directionare increased by 1.

After performing such reset procedure, the transmitter and receiver bothhave the same HFN, and the encoding and decoding procedures areperformed with this HFN.

Hereafter, the re-establishment procedure in the AM RLC entity relatedto the present invention will be described.

The RLC re-establishment procedure is performed upon instructions fromthe RRC entity. For the AM RLC entity, re-establishment may be performedfor both directions (i.e., the transmitter direction and receiverdirection), or only for one direction among the transmitter direction orthe receiver direction. The following operations are performed accordingto commands of the RRC.

1. The state variables are initialized and values that can be set arethen set.

2. The HFN value of the receiver direction is set according to the valueinstructed from a higher level.

3. The Control PDU(s) of the transmitter and receiver are deleted, andthe AMD PDU(s) of the receiver are deleted.

Re-establishment in the transmitter direction of the RLC entity isperformed in the following manner.

1. The state variables are initialized and values that can be set arethen set.

2. The HFN value of the receiver direction is set according to the valueinstructed from a higher level.

3. For re-establishment only in the transmitter direction, performprocedure from step 4. For re-establishment of both the transmitter andthe receiver, perform procedure from step 6.

4. The Control PDU(s) of both transmitter and receiver are all deleted,and among the SDUs in the transmitter, those SDUs that have beencompletely transmitted are deleted.

5. The SDU(s) not deleted in step 4 are re-segmented again according tothe set RLC size. Then, step 7 is performed.

6. The Control PDU(s) of both the receiver and transmitter are deleted,and the AMD PDUs in the transmitter are deleted.

7. The timers, excluding Timer_poll_periodic and Timer_status_periodic,are stopped.

In the related art, when the RLC re-establishment procedure isperformed, all Control PDU(s) are deleted even if the re-establishmentis for a single direction (i.e. either the transmitting direction or thereceiving direction). However, this may not be desirable in certainsituations.

DISCLOSURE OF INVENTION Technical Problem

In the related art, when the RLC re-establishment procedure isperformed, all Control PDU(s) are deleted even if the re-establishmentis for a single direction (i.e. either the transmitting direction or thereceiving direction). However, this may not be desirable in certainsituations.

Technical Solution

The present invention has been developed in order to solve at least theabove described problems of the related art that deletes all controlPDUs for both directions of re-establishment. As a result, the presentinvention provides an efficient AM RLC re-establishment mechanism(scheme) that deletes only those control PDUs related to a particularre-establishment direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary UMTS network architecture applicable to therelated art and the present invention.

FIG. 2 shows an exemplary radio protocol architecture used in UMTS.

FIG. 3 shows an exemplary structure of an AM RLC PDU that is a data PDUused when data is transmitted.

FIG. 4 shows an exemplary structure of a Status PDU.

FIG. 5 shows an exemplary structure of a Piggyback Status PDU.

FIG. 6 shows an exemplary structure of a Reset/Reset Ack PDU.

FIG. 7 shows an inefficient a single-sided (one direction)re-establishment procedure that occurs during a RLC Reset process.

FIG. 8 shows an exemplary flow chart of a RLC re-establishment method ina radio communication system according to the present invention.

MODE FOR THE INVENTION

One aspect of the present invention is the recognition by the presentinventors regarding the problems and drawbacks of the related artdescribed above and explained in more detail hereafter. Based upon suchrecognition, the features of the present invention have been developed.

The concepts and features of the present invention may be generallydescribed as follows:

First, it should be noted that there may be many reasons why RLCre-establishment must be performed. One example would be when a mobileterminal (UE) is initially under the control of a first radio networkcontrol (RNC) but later falls under the control of a second RNC. Asdifferent manufacturers produce their own radio network controllers(RNCs), each RNC would use its own types of parameters, leading tocompatibility problems.

Another example where RLC re-establishment (for an RLC of the UE, an RLCof the network, or both) would be needed is when a cell (or coveragearea) contains different regions that can support different accesstechniques. For instance, with respect to a single cell, at locationsnear the center of the cell, the UE may be able to perform high speedaccess (such as HSDPA and/or HSUPA) with the network, but at locationsnear the boundary (or edge) of the cell, such high speed access may notbe available. As the UE moves within a single cell, moves between two ormore cells, moves between different types of networks, etc., RLCre-establishment should be performed in order to support seamlesscommunications.

In the related art, when re-establishment (i.e., AM RLCre-establishment) is performed, the control information related to boththe transmitting side and the receiving side are deleted. Namely, thereis no distinction in handling control information based on the directionof re-establishment.

In contrast, according to the present invention, the control informationis managed depending upon the direction in which re-establishment isperformed. Namely, when a single-sided re-establishment is performed,the control information (e.g., control PDUs) related to that directionis not deleted, which is different than the related art wherein allcontrol information is deleted regardless of the re-establishmentdirection.

The above general concepts and features will be described in more detailwith respect to various embodiments of the present invention.

When the related art RLC re-establishment procedure is performed, allControl PDU(s) are deleted even if the re-establishment is for a singledirection (i.e. either the transmitting direction or the receivingdirection). In most cases, such does not significantly affect the datatransmission capabilities of the mobile terminal or of the network. Thisis because, in most instances, when re-establishment is performed forboth the receiving direction and the transmitting direction, the contextof the RLC can only change because the Node B has changed or because theRNC has changed, and thus it is faster to newly start processing bydisregarding all control message information. Also, doing so removes thepossibility of inconsistencies (i.e., non-correspondence) in the contextof the transmitter and of the receiver.

The related art re-establishment method may be sufficient for certainsituations. However, as HSDPA (High Speed Downlink Packet Access) andHSUPA (High Speed Uplink Packet Access) techniques are being introduced,situations for RLC re-establishment frequently occur. An example wouldbe when a mobile terminal, located (camped) within one cell, isinitially located at a center of the cell but moves to the boundary (oredge) of the cell.

Namely, when the mobile terminal is at a central region of the cell, AMRLC PDU(s) having a relatively large size may be used, but when locatedat a cell boundary, the quality of the radio environment is degraded,and thus, relatively large sized AM RLC PDU(s) cannot be used.Accordingly, when the mobile terminal moves from a center of the cell toa cell boundary, or vice versa, despite the fact that the mobileterminal remains within the same cell, there is a need to change thesize of the AM RLC PDU(s) used by the mobile terminal. The introductionof HSDPA and HSUPA has allowed various types of physical channels andtransport channels to be used, and AM RLC PDU(s) having an optimal sizefor each physical channel or each transport channel can be used. As thesize of the AM RLC PDU(s) changes, the RLC entity must bere-established.

However, in such case, the uplink and the downlink do not always changetogether. This is due to the fact that the downlink quality and theuplink quality may be different (i.e., distinct). Namely, the degree ofdegradation on the downlink does not result in the same degree ofdegradation on the uplink. Thus, when a mobile terminal that uses bothHSDPA and HSUPA moves from the center of the cell to its boundary oredge, situations where the downlink quality is degraded to a level whereHSDPA cannot be used, but where HSUPA may still be used occur quitefrequently. As such, situations where the HSUPA quality is degraded yetthe HSDPA quality remains satisfactory, or when the mobile terminalmoves from a cell boundary to the cell center, as well as many othersituations may occur. In such cases, re-establishment for both thetransmitter direction and the receiver direction are not necessary, andonly re-establishment for the corresponding direction (e.g., only forthe uplink or only for the downlink) would be needed.

However, in the related art, even in those situation wherere-establishment for one direction is necessary, all control PDU(s) forthe transmitter direction and for the receiver direction are deleted.This results in serious problems in data transmission efficiency asshown in the following example.

FIG. 7 shows a re-establishment method while the Reset procedure is inprogress.

1. The Reset procedure begins from the transmission direction of side A.A Reset PDU is transmitted, and a Reset PDU is received in the receptiondirection of side B.

2. The receiver direction of side B forms the Reset Ack PDU with respectto the Reset PDU and waits for transmission.

3. Simultaneously with the procedure of step 2, the re-establishmentprocedure with respect to one direction is performed. At side B, there-establishment procedure for the transmitter direction occurs, andaccordingly, at side A, the re-establishment procedure for the receiverdirection occurs.

4. According to the related art, even if only the re-establishmentprocedure for the transmitter direction occurs at side B in step 3, allControl PDUs must be deleted. Thus, the Reset Ack PDU(s) formed duringstep 2 but not yet transmitted must be deleted. Here, the Reset Ack PDUis a PDU formed at the receiver of side B, and does not affect thetransmitter of side B.

5. Side A waits for a response to the Reset PDU that was sent in step 1,but at side B, because the Reset Ack PDU was already deleted, side Acannot receive a response from side B. Thus, side A transmits a ResetPDU upon lapse of a certain time or when a new condition is satisfied.

In the above procedure, the Reset procedure must be handled quickly.Through the Reset procedure, each side exchanges HFNI values and thelike and works towards normalizing communications. For example, if theHFN values used respectively for the directions of the receiver of sideB and the transmitter of side A are different, data cannot be properlydecoded at the receiver. Thus, the Reset procedure should be terminatedas quickly as possible. However, the Reset procedure can be terminatedonly if a Reset Ack PDU is properly received by the transmitter. In theabove process, even though re-establishment occurred in the directionthat is unrelated to the Reset, because both the transmitter and thereceiver deleted all Control PDUs, the procedure for normally exchangingControl PDUs is delayed.

This results in preventing data transmission and reception while theReset procedure is being performed, and the data transmission rate isnot only degraded, but also, correction of important state variablessuch as HFNI is prevented, which leads to problems of disruptedcommunications.

Accordingly, the present invention provides an improved operation of anAM RLC entity for a single-sided RLC re-establishment, which increasesdata transmission rate and minimizes communication disruptions.

In the present invention, during the single-sided RLC re-establishmentprocedure, the transmitting side and the receiving side only deletes theControl PDU(s) related to its respective direction.

Namely, when the receiving side of the AM RLC entity is re-established,the RLC entity only deletes those Control PDU(s) related to thereceiving direction, while the Control PDU(s) related to thetransmitting direction are not deleted.

Similarly, when the transmitting side of the AM RLC entity isre-established, the RLC entity only deletes those Control PDU(s) relatedto the transmitting direction, while the Control PDU(s) related to thereceiving direction are not deleted.

Here, the Control PDU(s) related to the transmitting side directionrefers to Control PDU(s) formed by the transmitting side of the RLCentity.

The Control PDU(s) formed by the transmitting side include ControlPDU(s), such as a Reset PDU or a MRW SUFI, that are to be actively sentby the transmitting side.

The Control PDU(s) formed by the receiving side include Control PDU(s),such as a Reset Ack PDU or a MRW Ack SUFI, that are to be actively sentby the receiving side.

In the above procedure, the Control PDU(s) not deleted are to betransmitted to the peer entity immediately. The main reason why aControl PDU remains in the RLC entity is because the Control PDU iswaiting in the buffer because the lower layer currently does not havethe appropriate transmission capability. As an easy example, assumingthat a certain RLC entity can transmit a PDU at every second, every 4seconds, every 7 seconds, etc., a Control PDU generated at 2 secondsmust wait 2 more seconds in order to be transmitted when 4 seconds isreached. However, during such wait time, a re-establishment proceduremay occur. In such case, in order to quickly terminate the procedures inprocess, it would be effective to immediately send the Control PDU (thatis waiting to be transmitted) as soon as the re-establishment occurs.Thus, among the Control PDU(s) that have not been transmitted, and notdeleted by the re-establishment procedure should be immediatelytransmitted to the peer RLC entity. Accordingly, such Control PDU(s)that remain without being deleted should be reserved for transmission.

Thus the present invention proposes that with respect to Control PDUsformed before a re-establishment procedure and reserved fortransmission, or Control PDUs not transmitted before there-establishment procedure and not deleted through the re-establishmentprocedure, new Control PDU(s) should be formed and its transmissionshould be scheduled again.

In other words, when a re-establishment procedure for the transmittingside occurs, the receiving side of the RLC entity does not delete allControl PDUs existing at that time, but only deletes those Control PDUsrelated to the receiving side (direction).

Put differently, the present invention proposes that whenre-establishment occurs, the receiving side of the RLC entity does notdelete all existing Control PDUs, but Control PDUs unrelated to thereceiving side (direction) are not deleted. Also, other Control PDUs areall deleted.

Put differently, the present invention proposes that whenre-establishment occurs, the receiving side of the RLC entity does notdelete all existing Control PDUs, but Control PDUs related to thetransmitting side (direction) are not deleted. Also, the Control PDUsunrelated to the transmitting side (direction) are all deleted.

Here, Control PDUs related to the receiving side (direction) may includeAcknowledgement Status Report, Window SUFI, MRW Ack SUFI, and the like.

Control PDUs unrelated to the receiving side (direction) may include MRWSUFI, Reset PDU, Reset Ack PDU, and the like.

Control PDUs related to the transmitting side (direction) may includeMRW SUFI and the like.

Control PDUs unrelated to the transmitting side (direction) may includeAcknowledgement Status Report, Window SUFI, MRW Ack SUFI, Reset PDU,Reset Ack PDU, and the like.

Next, an example of an RLC entity operation in the RLC re-establishmentprocedure according to the present invention will be described.

FIG. 8 shows an exemplary flow chart of a RLC re-establishment method ina radio communication system according to the present invention.

1. The state variables are initialized and values that can be set arethen set.

2. The HFN value of the receiving direction is set according to thevalue instructed from a higher level.

3. The receiving direction AMD PDUs are deleted.

4. If re-establishment is only in the receiving direction, then amongthe remaining Control PDUs, the Control PDUs excluding the transmittingdirection Control PDUs are deleted.

5. The remaining Control PDUs are formed as new Control PDUs

Here, the most important transmitting side Control PDUs are MRW SUFI andReset PDU. As the MRW SUFI and Reset PDU are formed as respectivelydifferent Control PDUs, an RLC entity operation in the receivingdirection re-establishment procedure is also proposed as follows:

1. The state variables are initialized and values that can be set arethen set.

2. The HFN value of the receiving direction is set according to thevalue instructed from a higher level.

3. The receiving direction AMD PDUs are deleted.

4. If re-establishment is only in the receiving direction, then amongthe remaining Control PDUs, if a MRW SUFI exists, that MRW SUFI isformed as a new Control PDU.

5. Among the remaining Control PDUs, if a Reset PDU exists, the ControlPDUs excluding the Reset PDU are deleted.

6. Any newly formed Control PDUs or Reset PDUs are reserved fortransmission.

From the viewpoint of MRW SUFI and other Control PDUs, Anotherembodiment of the present invention is as follows:

1. The state variables are initialized and values that can be set arethen set.

2. The HFN value of the receiving direction is set according to thevalue instructed from a higher level.

3. The receiving direction AMD PDUs are deleted.

4. If re-establishment is only in the receiving direction, theAcknowledgement Status Report, Window SUFI, MRW Ack SUFI, Reset PDU, andReset Ack PDU are deleted.

5. After the above step, among the remaining Control PDUs, if a MRW SUFIexists, that MRW SUFI is formed as a new Control PDU.

6. New Control PDUs are reserved for transmission.

In the above step 5, the MRW SUFI is merely one example, and regardlessof the receiving direction, namely, Control PDUs or SUFI that wereformed before re-establishment, not transmitted before re-establishment,and not deleted during re-establishment are all formed as new PDUs instep 5 and transmitted in step 6.

In the above examples, the existence of a Reset PDU means that a Resetprocedure is in progress. Thus, in such case, reserving transmission ofa Reset PDU means that a new reset procedure is started after there-establishment procedure. The present invention proposes that for are-establishment procedure only in the receiving direction, all ControlPDUs excluding the MRW SUFI are deleted, and if there was a Reset PDU(i.e., when a Reset procedure was in progress), the Reset procedure isnewly started. Here, Control PDUs excluding the MRW SUFI, refers to anAcknowledgement Status Report, Window SUFI, MRW Ack SUFI, and Reset PDU,Reset Ack PDU.

In summary, the receiving direction operation according to the presentinvention is as follows:

1. The state variables are initialized and values that can be set arethen set.

2. The HFN value of the receiving direction is set according to thevalue instructed from a higher level.

3. The receiving direction AMD PDUs are deleted.

4. If re-establishment is only in the receiving direction, theAcknowledgement Status Report, Window SUFI, MRW Ack SUFI, Reset PDU, andReset Ack PDU are deleted.

5. After the above steps, if there are any remaining Control PDUs thatwere formed before re-establishment, not transmitted before there-establishment procedure, and not deleted in step 4, such Control PDUsare formed as new Control PDUs.

6. The newly formed Control PDU(s) are reserved for transmission.

7. In step 4 above, if there was a Control PDU that was deleted, namely,if there was a Reset procedure in progress before the re-establishmentprocedure, a Reset PDU is formed and transmitted. Namely, a new Resetprocedure is started.

In other words, when a re-establishment procedure occurs (for thetransmitting side direction), the transmitting side of the RLC entitydoes not delete all Control PDUs existing at that time, but only deletesthose Control PDUs related to the transmitting side (direction).

Put differently, the present invention proposes that whenre-establishment occurs (for the transmitting side direction), thetransmitting side of the RLC entity does not delete all existing ControlPDUs, but Control PDUs unrelated to the transmitting side (direction)are not deleted. Also, other Control PDUs are all deleted.

Put differently, the present invention proposes that whenre-establishment occurs (for the transmitting side direction), thetransmitting side of the RLC entity does not delete all existing ControlPDUs, but Control PDUs related to the receiving side (direction) are notdeleted. Also, the Control PDUs unrelated to the receiving side(direction) are all deleted.

Here, Control PDUs related to the transmitting side (direction) mayinclude MRW SUFI, and the like.

Control PDUs unrelated to the transmitting side (direction) may includeAcknowledgement Status Report, Window SUFI, MRW Ack SUFI, Reset PDU,Reset Ack PDU, and the like.

Control PDUs related to the receiving side (direction) may includeAcknowledgement Status Report, Window SUFI, MRW Ack SUFI, and the like.

Control PDUs unrelated to the receiving side (direction) may include MRWSUFI, Reset PDU, Reset Ack PDU, and the like.

In one embodiment, the present invention proposes the followingoperations when the transmitting side (direction) of the RLC isre-established:

1. The state variables are initialized and values that can be set arethen set.

2. The HFN value of the transmitting direction is set according to thevalue instructed from a higher level.

3. For re-establishment only in the transmitting direction, performprocedure from step 4. For re-establishment of both the transmitter andthe receiver, perform procedure from step 9.

4. Among the SDUs in the transmitting side, the SDUs that have beencompletely transmitted are deleted.

5. Among the Control PDUs existing in the RLC entity, if a MRW Ack SUFIexists, that MRW Ack SUFI is formed as a new Control PDU.

6. After step 5, except for the Reset Ack PDU among the remainingControl PDUs, all Control PDUs are deleted. Namely, among the ControlPDUs formed before the re-establishment procedure, all Control PDUs(except the Reset Ack PDU) are deleted.

7. The SDUs not deleted as a result of step 4 are re-segmented againaccording to the set RLC size.

8. Perform procedure from step 10.

9. The Control PDU(s) of both the receiver and transmitter are deleted,and the AMD PDUs in the transmitter are deleted.

10. The timers, excluding Timer_poll_periodic and Timer_status_periodic,are stopped.

As another embodiment, the present invention proposes the followingoperations when the transmitting side (direction) of the RLC isre-established:

1. The state variables are initialized and values that can be set arethen set.

2. The HFN value of the transmitting direction is set according to thevalue instructed from a higher level.

3. For re-establishment only in the transmitting direction, performprocedure from step 4. For re-establishment of both the transmitter andthe receiver, perform procedure from step 9.

4. Among the SDUs in the transmitting side, the SDUs that have beencompletely transmitted are deleted.

5. Among the Control PDUs existing in the RLC entity, all Control PDUs(excluding the Control PDUs related to the receiving direction) aredeleted.

6. After step 5, the remaining other Control PDUs are formed as newControl PDUs and transmission is reserved.

7. The SDUs not deleted as a result of step 4 are re-segmented againaccording to the set RLC size.

8. Perform procedure from step 10.

9. The Control PDU(s) of both the receiver and transmitter are deleted,and the AMD PDUs in the transmitter are deleted.

10. The timers, excluding Timer_poll_periodic and Timer_status_periodic,are stopped.

In the above examples, the existence of a Reset Ack PDU means that aReset procedure is in progress. Thus, in such case, reservingtransmission of a Reset Ack PDU means that a reset procedure is startedafter the re-establishment procedure. The present invention proposesthat for a re-establishment procedure only in the transmittingdirection, all Control PDUs (excluding Control PDUs related to thereceiving direction) are deleted, and if there was a Reset Ack PDU(i.e., when a Reset procedure was in progress), the Reset procedure isnewly started. Here, Control PDUs excluding those related to thereceiving direction, refers to MRW SUFI, and Reset PDU, Reset Ack PDU.

In summary, the transmitting direction operation according to anotherembodiment of the present invention is as follows:

1. The state variables are initialized and values that can be set arethen set.

2. The HFN value of the receiving direction is set according to thevalue instructed from a higher level.

3. For re-establishment only in the transmitting direction, performprocedure from step 4. For re-establishment of both the transmitter andthe receiver, perform procedure from step 10.

4. Among the SDUs in the transmitting side, the SDUs that have beencompletely transmitted are deleted.

5. Among the Control PDUs existing in the RLC entity, all Control PDUs(excluding those Control PDUs related to the receiving direction) aredeleted. Here, the Control PDUs related to the receiving direction areControl PDUs that inform about the receiving side circumstances. Forexample, an Acknowledgement Status Report that indicates which PDUs wereproperly received or not received, a Window SUFI that adjusts the windowsize that can be received, a MRW Ack SUFI that is a response message ofthe receiving side that is sent for a MRW SUFI that informs about theSDU information discarded at the transmitting side, and the like.

6. After the above steps, if there are any Control PDUs that were formedbefore the re-establishment procedure, or that were not transmittedbefore the re-establishment procedure and still remain without beingdeleted in step 5, such are formed as new Control PDUs.

7. In the above step, transmission of the newly formed Control PDUs isreserved.

8. The SDUs not deleted as a result of step 4 are re-segmented againaccording to the set RLC size.

9. Perform procedure from step 11.

10. The Control PDU(s) of both the receiver and transmitter are deleted,and the AMD PDUs in the transmitter are deleted.

11. The timers, excluding Timer_poll_periodic and Timer_status_periodic,are stopped.

In the above operation, the procedure of deleting the SDUs that havebeen completely transmitted among those of the transmitting direction,is only performed when on the transmitting direction is re-established.But when considering the situation where both directions are actuallyre-established, such re-establishment of both directions can beconsidered as initializing the RLC entity itself, and thus theoccurrence of the above steps may be changed.

Also, in step 8 described above, the re-segmentation of data PDUs isunrelated to the Control PDUs, thus is not affected by sequential order.For example, step 8 can be performed right after step 4.

As described above, the present invention provides a method wherein, ifthe RLC entity is re-established, all Control PDUs are not deletedregardless of whether re-establishment is only for one direction, butonly those Control PDUs related to a particular direction areselectively deleted, and the Control PDUs newly formed afterre-establishment are immediately transmitted. As a result, thecommunication disconnection time is reduced, the RLC data transmissionrate is improved, etc. to thus improve user satisfaction.

The present disclosure provides a re-establishment method for anAcknowledged Mode Radio Link Control entity, the method comprising:receiving, from an upper entity, a command to perform Acknowledged ModeRadio Link Control re-establishment; and managing control protocol dataunits by considering a direction of the Acknowledged Mode Radio LinkControl re-establishment. The control protocol data units related to thedirection are deleted. The control protocol data units not related tothe direction are not deleted. The method may further comprise:scheduling the control PDUs for transmission after acknowledged moderadio link control re-establishment. The upper entity is a RadioResource Control layer. The Acknowledged Mode Radio Link Controlre-establishment is performed in a transmitting direction. TheAcknowledged Mode Radio Link Control re-establishment is performed in areceiving direction.

Also, the present disclosure provides a scheme for re-establishment of aradio link control entity, the scheme comprising: deciding to performre-establishment of a protocol entity; and processing controlinformation by considering the direction of the re-establishment of theprotocol entity. The protocol entity is an Acknowledged Mode Radio LinkControl entity. The deciding is based upon a command received from anupper layer entity. The control information is in the form of controlprotocol data units. The Acknowledged Mode Radio Link Controlre-establishment is performed in a transmitting direction. TheAcknowledged Mode Radio Link Control re-establishment is performed in areceiving direction.

Additionally, the present disclosure provides a protocol stack tosupport re-establishment of a radio link control entity, the protocolstack comprising: a Radio Resource Control layer adapted to provideinstructions to perform re-establishment of a lower layer; and a RadioLink Control layer cooperating with the Radio Resource Control layer andadapted to perform re-establishment based upon the instructions from theRadio Resource Control layer by considering a direction of there-establishment.

It should be noted that the features of the present invention arerelated to issues regarding the enhancement and evolution of the 3GPPstandard. As such, the 3GPP TS 25.322 and its related sections orportions thereof, as well as various developing enhancements thereofpertain to the present invention. It can be clearly understood that thelabeling and terminology used to describe the present invention aremerely exemplary and thus may be altered (or later clarified) as aresult of ongoing or future discussions.

This specification describes various illustrative embodiments of thepresent invention. The scope of the claims is intended to cover variousmodifications and equivalent arrangements of the illustrativeembodiments disclosed in the specification. Therefore, the followingclaims should be accorded the reasonably broadest interpretation tocover modifications, equivalent structures, and features that areconsistent with the spirit and scope of the invention disclosed herein.

1. A re-establishment method for an Acknowledged Mode Radio Link Controlentity, the method comprising: receiving, from an upper entity, acommand to perform Acknowledged Mode Radio Link Controlre-establishment; and managing control protocol data units byconsidering a direction of the Acknowledged Mode Radio Link Controlre-establishment.
 2. The method of claim 1, wherein control protocoldata units related to the direction are deleted.
 3. The method of claim1, wherein control protocol data units not related to the direction arenot deleted.
 4. The method of claim 3, further comprising: schedulingthe control PDUs for transmission after acknowledged mode radio linkcontrol re-establishment.
 5. The method of claim 1, wherein the upperentity is a Radio Resource Control layer.
 6. The method of claim 1,wherein the Acknowledged Mode Radio Link Control re-establishment isperformed in a transmitting direction.
 7. The method of claim 1, whereinthe Acknowledged Mode Radio Link Control re-establishment is performedin a receiving direction.
 8. A scheme for re-establishment of a radiolink control entity, the scheme comprising: deciding to performre-establishment of a protocol entity; and processing controlinformation by considering the direction of the re-establishment of theprotocol entity.
 9. The scheme of claim 8, wherein the protocol entityis an Acknowledged Mode Radio Link Control entity.
 10. The scheme ofclaim 9, wherein the deciding is based upon a command received from anupper layer entity.
 11. The scheme of claim 10, wherein the controlinformation is in the form of control protocol data units.
 12. Themethod of claim 11, wherein the Acknowledged Mode Radio Link Controlre-establishment is performed in a transmitting direction.
 13. Themethod of claim 11, wherein the Acknowledged Mode Radio Link Controlre-establishment is performed in a receiving direction.
 14. A protocolstack to support re-establishment of a radio link control entity, theprotocol stack comprising: a Radio Resource Control layer adapted toprovide instructions to perform re-establishment of a lower layer; and aRadio Link Control layer cooperating with the Radio Resource Controllayer and adapted to perform re-establishment based upon theinstructions from the Radio Resource Control layer by considering adirection of the re-establishment.